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Null Case Study: 29 November 2001

Null Case Study: 29 November 2001. Case Overview. Vigorous 500 hPa trough/ULJ entrance region Strong surface cold front moved slowly east 4 tornado watches issued from central TN to Gulf Coast 31 high wind/hail reports, but no tornadoes. SPC Convective Outlook 28/0600 UTC.

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Null Case Study: 29 November 2001

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  1. Null Case Study:29 November 2001

  2. Case Overview • Vigorous 500 hPa trough/ULJ entrance region • Strong surface cold front moved slowly east • 4 tornado watches issued from central TN to Gulf Coast • 31 high wind/hail reports, but no tornadoes

  3. SPC Convective Outlook 28/0600 UTC ...WRN GULF COASTAL STATES INTO THE MID MS/TN VLYS... …GIVEN THE SLOWER MODEL SOLUTIONS...IT APPEARS THAT THE STRONGER DYNAMICS WILL WAIT UNTIL JUST BEYOND THE DAY 1 PERIOD TO AFFECT THE CNTRL GULF COASTAL AREAS. NONETHELESS...POTENTIAL DOES EXIST FOR THE DEVELOPMENT OF A SQUALL LINE AROUND 29/12 UTC ACROSS SCNTRL MS ACROSS SERN LA INTO THE NWRN GULF OF MX. AT THAT POINT...WIND AND TORNADO POTENTIAL WILL INCREASE THURSDAY.

  4. Tornado Watches 29 Nov. 2001 WATCH TIMES (all for 29 Nov. 2001) 838: 1415-1900 UTC 839: 1600-2100 UTC 840: 1800-2300 UTC 841: 1900-0000 UTC 841 838 840 839

  5. Severe Wx. Reports 29 Nov. 2001

  6. 29 Nov. 2001 1200 UTC DT  and Winds

  7. Forcing due to differential CVA

  8. Forcing due to WAA

  9. 700 hPa Ascent 29/1200 UTC

  10. 200 hPa jet and cross section

  11. L 29/1200 UTC

  12. L 29/1500 UTC

  13. Surface Frontogenesis 29/1200 UTC

  14. CAPE 29/1500 UTC

  15. RUC Sounding Location 1 MUCAPE 1295 J kg-1 SBCAPE 0 J kg-1 0-6 km shear 32 m s-1 0-2 km shear 8 m s-1

  16. RUC Sounding Location 3 MUCAPE 1819 J kg-1 SBCAPE 1819 J kg-1 0-6 km shear 16 m s-1 0-2 km shear 8 m s-1

  17. Summary: Case Study • Potent upstream trough provided little synoptic-scale ascent due to term cancellation • ULJ entrance region source of lift in NW Mississippi • Strengthening surface front source of mesoscale lift (esp. in SW Mississippi) • Instability ahead of front was elevated where best lift was (NW Mississippi)

  18. Summary: Case Study • Cloud cover in eastern Mississippi inhibited SBCAPE • SB CAPE was in SW Mississippi where low-level veering & 0-6 km shear were much weaker than in NW Mississippi • Linear/bowed segments resulted in wind damage but no tornadoes

  19. Question • Were the tornado watches issued by SPC warranted to warm public of potential danger?

  20. L 29/1500 UTC

  21. Conclusions

  22. Conclusions: • Nocturnal cool season tornado phenomenon along Gulf coast exists • Climatologically favorable 0-1 km shear profile exists along coastline at night: • Nocturnal LLJ maximized at coast at ~ 1000 m • Surface winds ‘back’ along coastline at night • This shear profile is enhanced when mid-latitude system moves across southeast US

  23. Most Favorable Supercell Hodograph Weisman and Rotunno 2000

  24. Conclusions cont’d: • Composites show common features: • ULJ entrance region at ~ 200 hPa • Vigorous upstream trough at 500 hPa • LLJ and e ridge at 850 hPa • Surface cyclone to west • Presence of highly anomalous (> 8C) surface moisture • Surface front or boundary nearby • Stronger features during nocturnal episodes

  25. Conclusions cont’d: • Both case studies show features similar to composite but only 1 resulted in tornado episode • Both had strong upper-level system to west • Both had strengthening surface front • Distinguishing factors may be: • CAPE distribution • 0-1 km shear profile where best CAPE/lift were located

  26. Future Work • More detailed investigation of null events • Composite based upon high risk outlook location • What about other types of severe weather (e.g., high wind, hail, flash flooding)? • How do ingredients necessary for southeast US nocturnal tornado episode compare to warm season Great Plains tornado episode?

  27. Acknowledgements • Lance • Committee: Dan Keyser, John Molinari, Chris Thorncroft, Russ Schneider, Morris Weisman • COMET • Grant Participants: Russ Schneider, Steve Weiss, Bob Johns, Geoff Manikin, Pat Welsh

  28. Acknowledgements (cont’d) • Celeste, Diana, Lynn, Sharon • Grad Students, past and present • Sheryl (Honikman) Thorp, Eyad Atallah, Kristen Corbosiero, Mike Notaro, Teresa Bals-Elsholz, Dan Meade, Tom Galarneau, Anantha Aiyyer • My Family: my parents and brother • Tom and Catherine

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